1. Field of the Invention
The present invention relates to an exhaust gas recirculation system, which recirculates exhaust gas of an internal combustion engine from an exhaust passage to an intake passage of the internal combustion engine.
2. Description of Related Art
The exhaust gas recirculation system (EGR system), which recirculates the exhaust gas of the internal combustion engine from the exhaust passage to the intake passage, is known. In this EGR system, a water-cooled exhaust gas cooler (EGR cooler), which uses coolant to cool the exhaust gas, is provided in an exhaust gas recirculation pipe (EGR pipe), through which the exhaust gas (EGR gas) is recirculated from the exhaust passage to the intake passage. With this EGR system, the combustion temperature of the engine can be advantageously reduced to reduce the amount of noxious components (e.g., NOx) contained in the exhaust gas without deteriorating the output power of the engine.
Furthermore, in the EGR system having the EGR cooler, the EGR gas is recirculated from the exhaust passage to the intake passage while bypassing the EGR cooler when the temperature of the coolant is low, for example, at the time of engine start or during the winter season. In the EGR system having the EGR cooler, a bypass passage is formed in an interior of a housing having a cooler installation surface, to which the EGR cooler is installed. The bypass passage recirculates the EGR gas, which is supplied into a valve receiving chamber of the housing, to the intake passage while bypassing the EGR cooler. In the valve receiving chamber, there is provided a bypass change valve assembly, in which a bypass change valve is rotatably provided to open or close the bypass passage.
With reference to FIGS. 16 and 17, in a previously known EGR cooler system (see, for example, Japanese Unexamined Patent Publication No. 2007-132305A), an EGR valve module, which has an EGR valve 102 and a mode change valve 103, is placed in a housing 101 having a cooler installation surface, to which an EGR cooler (not shown) is installed. The EGR valve 102 variably controls the flow quantity of the EGR gas, which flows through the EGR gas passage. The mode change valve 103 changes the flow of the EGR gas between a cooler mode (cooled mode) for conducting the EGR gas through the EGR cooler and a bypass mode (hot bode) for conducing the EGR gas through a bypass passage 13 that bypasses the EGR cooler.
The EGR valve 102 is driven by an electric motor provided in an actuator main body 105 through a rotatable shaft 104, which supports the EGR valve 102.
The actuator main body 105 is a housing, an opening of which is closed with the sensor cover 49. The actuator main body 105 receives the electric motor (e.g., a DC motor) and a drive force transmission mechanism (e.g., a speed reducing gear mechanism). The electric motor generates a drive force upon receiving an electric power. The drive force transmission mechanism transmits the drive force of the electric motor to the rotatable shaft 104. That is, the actuator main body 105 forms an electric actuator, which includes the electric motor and the drive force transmission mechanism.
The mode change valve 103 is driven by a negative pressure driven actuator (not shown) through a rotatable shaft 106, which supports the mode change valve 103. The mode change valve 103 changes the operational mode between the cooler mode (FIG. 16) and the bypass mode (FIG. 17). In the cooler mode (FIG. 16), first and second EGR gas passages 11, 12, which are communicated with an inlet and an outlet, respectively, of the EGR cooler, are formed in the interior of the housing 101. In the bypass mode (FIG. 17), the bypass passage 13, which bypasses the EGR cooler, is formed in the interior of the housing 101.
The negative pressure driven actuator introduces the negative pressure, which is supplied from an electric vacuum pump, to a negative pressure chamber through a negative pressure control valve, so that a diaphragm is displaced in a plate thickness direction of the diaphragm due to a pressure difference between the negative pressure chamber and an atmospheric pressure chamber, and thereby a rod, which is synchronized with the diaphragm, is axially displaced. When the axial displacement of the rod is transmitted to the rotatable shaft 106 through a link plate, the rotatable shaft 106 is rotated for a predetermined angle. In this way, the valve position of the mode change valve 103 is changed.
In the exhaust gas recirculation system of Japanese Unexamined Patent Publication No. 2007-132305A, the EGR valve 102 and the mode change valve 103 are placed in the housing 101 having the cooler installation surface, to which the EGR cooler is installed to form the EGR valve module. In this instance, the electric actuator, which drives the EGR valve 102, and the negative pressure driven actuator, which drives the mode change valve 103, need to be separately provided. The provision of the two actuators disadvantageously results in an increase in the number of the components, so that the product costs may be disadvantageously increased.
Furthermore, the two actuators are provided to the housing such that the actuators protrude from the outer wall surface of the housing. Therefore, the entire size of the EGR valve module is increased, and thereby the required installation space for installing the EGR valve module on the vehicle is disadvantageously increased.
In view of the above disadvantage, it is conceivable to integrate the actuator, which drives the EGR valve 102, and the actuator, which drives the mode change valve 103, into a single negative pressure driven actuator.
However, the mode change valve 103, which is a two-position valve that changes between the cooler mode and the bypass mode, is disadvantageously synchronized with the actuator, which changes the rotational angle of the EGR valve 102 to continuously change the opening degree of the EGR gas passage. Therefore, it is difficult to satisfy both of the function of the EGR valve 102 and the function of the mode change valve 103.
For instance, even in the case where the mode change valve 103 is synchronized with the EGR valve 102 up to a predetermined location and is then desynchronized from the drive mechanism of the EGR valve 102, it is still difficult to displace the mode change valve 103 out of the range, within which the mode change valve 103 has an influence on the operation of the EGR valve 102. Furthermore, it is difficult to maintain such a position, and it is also difficult to implement the structure, which synchronizes the EGR valve 102 and the mode change valve 103.
The exhaust gas, which is outputted from the combustion chamber of the internal combustion engine, contains fine particulate impurities (exhaust fine particles, particulate matter), such as combustion residues or carbon particles. Therefore, the deposit of the particulate impurities contained in the EGR gas may possibly be adhered or accumulated at the interior of the housing 101 during the operation of the engine.
In the case where the deposit is adhered or accumulated around the EGR valve 102 and the mode change valve 103, when a viscosity of the deposit becomes relatively high upon dropping of the temperature of the deposit after engine stop, the EGR valve 102 and the mode change valve 103 may possibly stick to the passage wall of the housing 101 due to the solidification of the deposit.
Therefore, for example, at the time of the engine start, the EGR valve 102, which sticks to the passage wall surface of the housing 101 due to the solidified deposit that is adhered or accumulated around the EGR valve 102, is driven back-and-forth to rotate the EGR valve 102 about the valve full close position of the EGR valve 102. Furthermore, the mode change valve 103, which sticks to the flow passage wall surface of the housing 101 due to the solidified deposit that is adhered to or accumulated around the mode change valve 103, is driven back-and-forth to rotate the mode change valve 103 about the bypass full close position or the bypass full open position. As discussed above, it is conceivable to implement the method for releasing the sticking of the EGR valve 102 or the mode change valve 103 or the method for pulling and releasing the EGR valve 102 or the mode change valve 103 from the deposit that is adhered or accumulated around the EGR valve 102 or the mode change valve 103.
However, in the case of synchronizing the EGR valve 102 and the mode change valve 103 of Japanese Unexamined Patent Publication No. 2007-132305A through use of the negative pressure driven actuator, the size of the negative pressure driven actuator is disadvantageously increased to effectively implement the releasing of the sticking (pulling and releasing) of the EGR valve 102 and the mode change valve 103 even in the state where the negative pressure, which serves as the drive power source, is the low negative pressure. Therefore, the entire size of the EGR valve module is further increased, and thereby the required installation space for installing the EGR valve module on the vehicle is further increased.
In addition, the deposit can be easily adhered to or accumulated around the valve (the EGR valve 102, the mode change valve 103), which is used in the EGR system, and the deposit can be easily solidified upon decreasing of the temperature. Therefore, it is required to provide the releasing torque or load for releasing the sticking of the EGR valve 102 or the mode change valve 103 from the passage wall surface of the housing 101.
However, when the EGR valve 102 and the mode change valve 103 need to be driven by the drive force of the single actuator installed to the outer wall surface of the housing 101, the size of the actuator becomes disadvantageously large. Therefore, the entire size of the EGR valve module is further increased, and thereby the required installation space for installing the EGR valve module on the vehicle is further increased.